1. Field of the Invention
The present invention relates to a catalyst and its use in a catalytic cracking process. More particularly, the present invention relates to a catalytic cracking catalyst having improved activity and selectivity for producing high octane number naphtha.
2. Description of the Prior Art
Hydrocarbon conversion catalysts comprising a zeolite dispersed in a siliceous matrix are known. See, for example U.S. Pat. No. 3,140,249 and U.S. Pat. No. 3,352,796.
A catalyst comprising a zeolite, an inorganic oxide matrix and inert fines, which may be alpha alumina, is known. See U.S. Pat. No. 3,312,615.
A catalyst comprising an amorphous silica-alumina, separately added alumina and a zeolite is known. See U.S. Pat. No. 3,542,670.
A catalyst comprising a zeolite, an amorphous hydrous alumina and alumina monohydrate is known. See U.S. Pat. No. 3,428,550.
To improve the steam and thermal stability of zeolites, it is known to produce zeolites having a low level of alkali metal content and a unit cell size less than about 24.45 Angstroms. See U.S. Pat. Nos. 3,293,192 and Re. 28,629 (Reissue of U.S. Pat. No. 3,402,996).
It is also known to treat hydrogen or ammonium zeolite with H.sub.2 O at a temperature ranging from about 800.degree. to about 1500.degree. F., and subsequently cation exchanging the steam and water treated zeolite with cations which may be rare earth metal cations. The method increases the silica to alumina mole ratio of the zeolite. See U.S. Pat. No. 3,591.488.
U.S. Pat. No. 3,676,368 discloses a rare earth exchanged-hydrogen faujasite containing from 6 to 14 percent rare earth oxides.
U.S. Pat. No. 3,957,623 discloses a rare earth exchanged zeolite having a total of 1 to 10 weight percent rare earth metal oxide.
U.S. Pat. No. 3,607,043 discloses a process for preparing a zeolite having a rare earth content of 0.3 to 10 weight percent.
U.S. Pat. No. 4,036,739 discloses hydrothermally stable and ammonia stable Y zeolite in which a sodium Y zeolite is ion exchanged to partially exchange sodium ions for ammonium ions, followed by steam calcination and a further ion exchange with ammonium to reduce the final sodium oxide content to below 1 weight percent, followed by calcination of the reexchanged product, or according to U.S. Pat. No. 3,781,199, the second calcination may be conducted after the zeolite is admixed with a refractory oxide.